The present disclosure teaches a system and a method to use a receive planar phased array antenna, for example, on a satellite or a high altitude platform, for orienting an antenna by determining a pointing error of the antenna or an attitude error of the antenna platform. The conventional approach for estimating a pointing error includes using a dedicated four-horn monopulse antenna. Usually, the four-horn monopulse antenna is used solely to estimate a pointing error. If an antenna pointing error can be determined otherwise, the monopulse antenna can be eliminated, and the size and weight of the satellite or high altitude platform can be reduced. Furthermore, for a platform moving relative to the Earth surface, the fixed monopulse antenna is impractical because the satellite or platform housing the fixed monopulse antenna is moving relative to a transmitter transmitting the known signal.
The prior art works well for geostationary satellites but does not work when the satellite or high altitude platform is in motion relative to earth. There is no prior art to maintain beams illuminating fixed cells on the ground when the platform is in motion, for example, for a Low Earth Orbit (LEO) satellite, a High Attitude Platform System (HAPS) or an aircraft antenna.